The present invention relates to life support equipment and methods for providing physiological protection to pilots and astronauts when subjected to high g-force maneuvers.
Modem aircraft are capable of maneuvers which can impose multiple gravity (xe2x80x9cgxe2x80x9d) forces which exceed the physiological protection provided by state of the art life support equipment. Such equipment includes an anti-g suit with pneumatic bladders surrounding a major portion of a pilot""s legs, thighs and abdomen, which when inflated impede the flow of blood to the lower extremities and abdomen. In addition, a chest bladder is often used to restrain excess chest expansion during the inhalation of oxygen (or oxygen enriched air) at elevated pressures. A mask, fitted over the pilot""s nose and mouth, receives oxygen or a mixture of oxygen and air under a pressure proportional to the g-force loading to which the pilot is subjected.
A typical anti-g equipment arrangement for use by combat and test pilots is illustrated in FIG. 1 in which a source 11 of a suitable gas, such as air under a suitable pressure from an aircraft""s compressor is connected to a pressure regulator 12. A source 10 of oxygen or oxygen enriched air (hereinafter collectively referred to as O2) under a suitable high pressure, e.g., 1.5 to 10.0 atmospheres or about 22 to 150 psi, is connected to separate pressure regulator 12. The regulator 12 supplies the air, via line 16, to a conventional anti-g suit 18 which fits over the legs and lower abdomen of the pilot. The anti-g suit includes a series of inflatable bladders 18a. The regulator 14 supplies O2 to a chest bladder 20 and a face mask 22 via line 24.
Conventional g-force sensors (not shown) control the regulators 12 and 14 so that the output pressures thereof are a function of the g-forces to which the pilot is being subjected. FIG. 2 illustrates, via curve 24, the typical pressure in millimeters, of Hg (ordinate) applied to the anti-g suit as a function of the g-force (abscissa). As is illustrated, the pressure curve 24 is essentially linear with changes in the g-force loading from about 1 g to about 10 g""s.
FIG. 3 illustrates, via curve 26, the typical pressure in inches of water (ordinate) applied to the chest bladder and the inlet to the mask as a function of the g-force loading. From about 4 g""s to 10 g""s the curve is essentially linear.
The mask 22 is provided with a conventional inhalation and exhalation valves (not shown). The exhalation valve remains closed until the pressure of the gas to be exhaled exceeds the positive pressure being supplied by the regulator 14. The pilot must therefore exert sufficient pressure on his or her lungs during the exhalation phase to overcome the positive supply pressure. The maximum exhalation pressure may exceed the supply pressure by 5 to 6 inches of H2O during a normal breathing cycle. A typical pilot""s inhalation and exhalation phases, using the conventional anti-g equipment, is illustrated in FIG. 4 where the line 28 represents one value of positive supply pressure (as measured along the ordinate) and the curve 30 represents the pressure in the mask during the pilot""s inhalation (t0-t1) and exhalation (t1-t2) phases. As is noted by the curve 30 the pressure in the mask follows a sinusoidal type curve during the breathing cycle. The extent of the fluctuations in mask pressure from the supply pressure depend on the gas capacity of the system and on the resistance of the mask regulator system. Such a state of the art system is discussed in several articles entitled Combined Advanced Technology Enhanced Design G-ensemble; Advanced Technology Anti G-Suit; and Combat Edge Aircrew Positive Pressure Breathing System published by the Brooks Scientific and Research Center of Space Medicine in San Antonio, Tex. and posted on its website at http://www.brooks.af.mil/HSW/products/edge.html.
At high g-forces, e.g., above 3-4 g""s, the state of the art anti-g equipment provides a constant positive pressure in the mask and vest. Such a pressure mode places little stress on a pilot""s system during inhalation. However, the positive pressure in the lungs and internal chest pressure causes the diaphragm to lower. In order to raise the diaphragm and help the breathing muscles to perform an exhalation and subsequent inhalation exercise it is necessary for the pilot to strain and release the abdominal muscles periodically. This is especially difficult at very high g-forces. With abdominal muscles in a strained condition and an impaired or non-functioning diaphragm, the breathing muscles cannot provide normal breathing. The exhalation and inhalation phases become shorter, i.e., the breathing rate and lung ventilation increase. The velocity of air flow through the exhalation valve increases during the shortened inhalation phase resulting in a higher resistance to exhalation which may reach 9-10 mm of mercury column. The increased stress not only causes the pilot to feel fatigue, but degrades his or her performance. At the same time blood slowly moves down from the brain as his or her higher heart rate indicates.
State of the art anti-g systems typically provide satisfactory physiological protection during force loads up to 8-9 g""s for only 30 to 40 seconds.
As a result, such conventional anti-g equipment will not accommodate the full performance capabilities of modem fighter aircraft. Thus, due to the limited time of high g tolerance, the pilot must restrict the aircraft""s performance to levels below its rated capabilities or run the risk of suffering sever fatigue at best or losing control of the aircraft at worst. In addition, the constant positive exhalation pressure at high g loads severely limits or precludes two-way radio communication with the attendant disadvantages thereof during maneuvering. Also pilots experience extreme discomfort when breathing at high g loads with the result that their physical condition may be impaired for some time after the cessation of a high g maneuver.
A pilot""s breathing rate is typically drastically increased by the higher exhalation resistance (FIG. 4), e.g., 40-50+ liters/min at 7-9 g force loads versus about 20 liters/min at no g load. Very often pilots complain of feeling severe pain in their hand joints due to the lack of compensating pressure. Immediately after long term exposure to high g forces, pilots have pointed out that their breathing does not return to normal for some time and that several days of rest may and often are required for rehabilitation after an intensive workout during flight. The long term effects on a pilot""s health resulting from the wear and tear on the organisms, e.g., those involved in the breathing and cardiovascular systems which results from regular g force overloads over an extended period have not been determined.
There is an urgent need to provide combat and test pilots with greater physiological protection from the effects of high g maneuvers.
In accordance with the present invention a pilot is equipped with an anti-g suit which is inflated from a pressurized gas, e.g., air, in accordance with the g forces being experienced by the pilot in a conventional manner.
A method and apparatus of overcoming the shortcomings of conventional anti-g equipment for providing physiological protection for pilots when subjected to high g-forces includes the use of an inhalation valve connected between a pressurized source of O2, an inlet/outlet port of the pilot""s face mask and a chest bladder.
An exhalation valve is connected between the inlet/outlet port and a low pressure region such as the aircraft cabin interior. The inhalation and exhalation valves are opened and closed, respectively, during the inhalation phase of the pilot""s spontaneous breathing cycle while the pressure of the O2 supplied to the inlet/outlet port is controlled so that the pressure rises from a predetermined minimum to a predetermined maximum as determined by the g force load to provide an increased volume of breathable O2 to the pilot""s lungs. The exhalation and inhalation valves are opened and closed, respectively, during the exhalation phase while the pressure in the inlet/outlet port is allowed to fall from the predetermined maximum to the predetermined minimum. The minimum pressure having a value less than the maximum for g-forces in excess of a selected value, e.g., 2.5-4 g""s,. Preferably the maximum pressure is within a range of about 7 to 10 inches of water at about a 2.5 g force and within a range of about 20 to 30 inches of water at about a 9 g force. The minimum pressure is preferably within a range of about 12 to 18 inches of water less than the maximum pressure for g-loads above about 4 g""s. The invention may employ a pneumatic system for controlling the functions (i.e., opening/closing) of the inhalation and exhalation valves as well as controlling the maximum and minimum pressures pursuant to a g-force sensor. Alternatively the invention may employ electrically operated variable flow (pressure) inhalation and exhalation valves responsive to the fluid flow path in the inlet/outlet port and the g force load as detected, for example, by a conventional electronic accelerometer. Optionally, the pressure of the gas supplied to the anti-g suit is nonlinear with respect to the g load over the anticipated g load range, e.g., the rate of pressure increase in the anti-g suit is higher during acceleration from low g loads to intermediate g loads and lower during acceleration from intermediate to high g-loads.
The present invention serves to maintain the parameters of a pilot""s circulation system in a permissible range for high g-forces thereby enabling the pilot to tolerate such g forces for extended periods with less stress. The present invention also enables a pilot to achieve improved performance while requiring considerably less rehabilitation time after flight as compared with the use of state of the art equipment.
The construction and operation of the present invention may be best understood in reference to the following description taken in conjunction with the accompanying drawings wherein like components are given the same reference number.